Many buildings, particularly relatively small buildings such as single-family houses, have a single HVAC unit that is controlled by a single thermostat. The HVAC unit typically comprises some type of fluid temperature modifying device, such as a furnace for heating air, a boiler for heating a liquid or steam, or an air conditioner having an evaporating coil for cooling air. If the fluid is air, it is typically ducted to various locations within the building, or if it is liquid or steam, it is typically piped to heat exchangers at various locations in the building. The thermostat in this type of space conditioning system is typically positioned at a location where the heating and cooling loads are representative of the entire structure. For example, the thermostat may be installed in an interior room away from windows and doors that would tend to influence the sensed temperature. The HVAC equipment then controls the heating and cooling of the entire structure according to the thermostat signal received from the single location.
However, a single thermostat location may not accurately represent the heating or cooling needs throughout the structure. Other locations of the building may have significantly greater or lower heating and cooling loads than exist at the location of the thermostat. For example, rooms having a larger surface area of windows, or rooms having exterior walls, may require greater heat inputs to maintain the desired temperature. Similarly, rooms facing south or west, or rooms that are on an upper story, may require greater cooling inputs to maintain the desired temperature. Where the HVAC equipment is controlled only by a single thermostat, the heating or cooling supplied to each individual area of the building will be based on the heating or cooling needs at the thermostat location and not on the actual heating and cooling needs of each individual area. As a consequence, the heating and cooling loads of individual areas of the structure may not be satisfied and the temperature of these areas will tend to deviate from the desired temperature.
In some situations, it may be desired to control different locations within a building at different temperatures. For example, rooms that are seldom occupied may not need to be maintained at the same temperature as rooms that are frequently occupied. Energy that is used to heat or cool these unoccupied rooms is not used effectively or economically. Also, rooms may be occupied by people having special temperature needs, such as an elderly person or an infant, that are preferably maintained at a different temperature than the rest of the building. However, a system that has only a single thermostat is generally unable to accurately control different locations in the building at different temperatures.
One known solution to this problem is to utilize HVAC zone control. Rather than having a single thermostat controlling the HVAC equipment, multiple thermostats are positioned at locations within the building that are expected to have different heating and cooling loads. Although it is possible that each of these thermostats could control a separate fluid temperature modifying device such as a separate furnace or air conditioner for each zone, such an approach is generally neither efficient nor economical. Rather, most commonly the ductwork or piping that is used to transmit the conditioned fluid to the building spaces is configured with controls to adjust fluid flow. For example, an air duct may be configured with a controllable damper that is capable of opening and closing to control the flow of air to a space within the building. Similarly, piping may be configured with a controllable valve that is capable of opening and closing to control the flow of liquid or steam to a space within the building.
A system having HVAC zone control generally requires the use of a zone controller to receive the signals from the various thermostats, control the operation of the heating or cooling device, and control the distribution of the conditioned fluid through the ductwork or piping. The zone controller typically comprises electronic circuitry for evaluating the heating or cooling needs of the various zones of the building and for determining an appropriate control of the heating or cooling device and the dampers or valves. While this control may be as simple as turning on the heating or cooling device and opening the damper or valve for a particular zone any time the thermostat from that zone calls for space conditioning, often times more complex control strategies are desired. For example, U.S. Pat. No. 5,024,265, incorporated in its entirety herein by reference, describes a zone control system having means for determining the zone of greatest demand and for synchronizing the start of the control signal for other zones to coincide with the start of the control signal for the zone of greatest demand. One advantage of this arrangement is that it may prevent overcycling of the heating or cooling device. Even relatively simple zone control schemes require substantial electronic circuitry to implement. Where more complex control strategies are used, even greater amounts of electronic circuitry are required. Regardless of the zone controller operating strategy used, zone controller electronic circuitry generally require a plurality of electronic components, such as wire receptacles, logic devices, relays, resistors, power supplies, and other electronic components for proper operation. The number of these electronic components tends to increase with increasing functionality and capacity of the zone controller.
There is a need for improved zone controllers.